U.S. Pat. No. 4,527,942 is incorporated herein by reference. This patent relates to a system for manipulating and positioning electronic test head loads. Through the proper application of counterbalances, the load unit is placed in a substantially weightless condition, whereby it may be manipulated and positioned quite easily and accurately.
In ordinary operation of such systems, after the load unit has been placed in the desired position, the load unit is locked in place. With such systems, if the balanced condition is lost while the load is locked in place and this fact is unknown to an operator of the system, upon release of the locking mechanism movable parts of the system will move in a rapid and uncontrolled manner. Such an unbalanced condition can result from loss of the counterbalancing weight, removal of the load unit, or failure of one of the components in the balancing portion of the system.